Knitted Spacer Fabric And Method For Producing Same

ABSTRACT

The invention relates to a knitted spacer fabric (10) and a method for producing same. The knitted spacer fabric (10) has a first layer (11) formed by stitches (13), a second layer (12) formed by stitches (13), and connection threads (21), which connect the two layers (11, 12) arranged at a distance from one another in a height direction (H). At least one predetermined separation point (22) is formed in each layer, at which point the tensile strength is reduced. The stitches (13) are formed in each case by a thread bundle comprising a first thread (16) and a second thread (17). The threads (16, 17) have different physical and/or chemical properties, for example different melting points, different resistances to alkaline or acidic agents, etc. The second thread (17) can thus be selectively severed at the at least one predetermined separation point (22) or weakened in respect of its tensile strength, whereas the at least one first thread (16) is not severed at the predetermined separation point (22) and preferably does not experience a significant reduction of its tensile strength.

RELATED APPLICATION(S)

This application claims the benefit of German Patent Application No. 20 2017 004 618.0, filed Aug. 22, 2017, and German Patent Application No. 10 2018 111 164.9, filed May 9, 2018, the contents of which is incorporated herein by reference as if fully rewritten herein.

TECHNICAL FIELD

The invention relates to a knitted spacer fabric which constitutes a three-dimensional textile structure. In contrast to textile fabrics, the knitted spacer fabric has two layers distanced in a height direction and each having a plurality of wales and courses, which layers are connected to one another by connection threads or pile threads. The knitted spacer fabric therefore forms a three-dimensional textile structure.

BACKGROUND

Knitted spacer fabrics of this kind are known and can be used for different applications. The knitted spacer fabric described in EP 1 860 218 A1 is to be easily separable at a predefined point. The wales in both layers of the knitted spacer fabric are connected to one another by weft threads. Here, stronger and weaker weft threads are used for the connection of the wales. A predetermined separation point can be formed between two wales in the longitudinal direction, parallel to the wales, as a result of the weaker weft threads.

The knitted spacer fabric described in DE 10 2008 046 437 A1 is constructed similarly to that in EP 1 860 218 A1. Pairs of wales arranged in a manner distributed uniformly over the width of the knitted spacer fabric in the direction of the courses are provided and are connected to a weaker weft thread and therefore each define a predetermined separation point in the direction of the wales.

For creating predetermined separation points in a transverse direction, substantially parallel to the courses, the knitted spacer fabric known from DE 10 2010 010 524 A1 comprises a main thread system and a further thread system in the two spaced-apart layers. The threads of the main thread system are more stable or tearproof than the threads of the additional thread system. At least one course is formed here by the stitches of the thread of the further thread system. The course has a lower stability and connects the two adjacent stitches of the wale, said stitches being formed by a thread of the main thread system. The course formed of the thread of the further thread system constitutes a predetermined separation point in the transverse direction parallel to the direction of extent of the courses.

Proceeding from the known knitted spacer fabrics, the object of the present invention is to achieve a predetermined separation point in the longitudinal direction and/or transverse direction of the knitted spacer fabric alongside a simple design.

SUMMARY

The knitted spacer fabric has a first layer comprising stitches and a second layer comprising stitches. The stitches in each layer form wales in a longitudinal direction and courses in a transverse direction. The longitudinal direction and the transverse direction are oriented at right angles to one another. The stitches are formed by a thread bundle, comprising a first thread and a second thread. The two threads are not intertwined, twisted, bonded to one another or directly connected to one another in some other way. For example, a thread feed of the knitting machine, in particular a guide needle, in order to form the thread bundle can feed the first thread and the second thread for stitch formation. The two threads are laid side by side.

In a height direction at right angles to the longitudinal direction and at right angles to the transverse direction, the two layers are arranged at a distanced from one another and are connected to one another by connection threads. A three-dimensional structure of the knitted spacer fabric is achieved as a result.

At least one predetermined separation point is formed in each layer. The at least one second thread, which either extends along the predetermined separation point or crosses the predetermined separation point is severed along the predetermined separation point or is at least weakened in respect of its tensile strength. The stitches of the first layer and the second layer can therefore tear very easily along the at least one predetermined separation point. The selective weakening of the second thread can be achieved for example physically or chemically after the knitting, for example by introducing energy in the form of heat into the knitted spacer fabric along the at least one predetermined separation point or for example by applying an agent, preferably a fluid. The chemical and/or physical properties of the first thread and of the second thread differ from one another, such that the second thread can be selectively weakened or severed at the predetermined separation point. The at least one first thread, which extends along the predetermined separation point or crosses the predetermined separation point, is maintained continuously in order to preserve the stitches in the layers and is unsevered at the at least one predetermined separation point.

The chemical and/or physical weakening of the second thread along the predetermined separation point can be achieved in principle over an arbitrary path or contour. Predetermined separation points of substantially any shape can thus be formed in the knitted spacer fabric. When applying a chemical substance a template can be used, for example in order to be able to selectively apply the substance for weakening or separating the at least one thread to the at least one predetermined separation point.

The predetermined separation point can thus be adapted very easily and in a versatile manner to be different requirements. For example, the predetermined separation point can correspond to the extent of an airbag flap. The knitted spacer fabric is used for instrument panels frequently as a lining for the leather surface or synthetic leather surface and must not hinder the opening of an airbag. The knitted spacer fabric according to the invention can be adapted easily and in a versatile manner to different shapes and sizes of the airbags.

In one embodiment the first thread and the second thread are made of different materials. Different chemical and/or physical properties are thus achieved, such that selective weakening of the second thread is possible and the stitch connection in the layers of the knitted spacer fabric along the predetermined separation points by the first thread is maintained.

In one exemplary embodiment the material of the first thread has a higher melting point than the material of the second thread. By introducing heat above the melting point of the second thread and below the melting point of the first thread, the second thread can be weakened selectively along the at least one predetermined separation point. The heat can be introduced in a contact-free manner, for example by means of electromagnetic radiation, preferably with use of a laser beam.

In one exemplary embodiment the material of the first thread can have a better alkali resistance than the material of the second thread. By applying an alkali substance, the second thread can be weakened or severed, wherein the first thread is not severed, so as to maintain the stitch formation. Alternatively or additionally, it is also possible that the material of the first thread has a better acid resistance than the material of the second thread. An acid substance can be applied along the at least one predetermined separation point in order to weaken the second thread.

So as not to sever the first thread by the application of an alkaline agent or acid, the alkaline agent or the acid can be washed out after a certain exposure time, such that although the second spread is weakened or severed along the predetermined separation point, the stitch formation by the first thread is in any case maintained.

It is advantageous if the first layer and/or the second layer is embodied without weft threads. Depending on the used connection method, the wales of the layers are connected to one another at least outside both by the first thread and by the second thread. The second thread can be severed along the predetermined separation point. A pillar stitch, tricot weave, linen weave, satin weave, twill or velvet lapping can be used as connection method in the first layer and/or in the second layer. The structure of the layers and production thereof is very simple, and it is possible to dispense with the use of a weft thread.

The connection threads are preferably arranged in such a way that they do not cross or pass through a predetermined separation space. The predetermined separation space is an area of the knitted spacer fabric that is defined by predetermined separation points, paired with one another, in the first layer and in the second layer. The predetermined separation space extends from the predetermined separation point in the first layer to the predetermined separation point in the second layer, which are preferably aligned with one another in the longitudinal direction and height direction. Adjacently to this predetermined separation space, the connection threads can be arranged for example without offset in the transverse direction, for example in the form of what is known as an I-loop.

In order to produce the above-described knitted spacer fabric, the following approach is adopted:

The knitted spacer fabric is firstly produced on a knitting machine. Here, the first thread and the second thread are fed without direct connection to one another for stitch formation. All stitches in the first layer and in the second layer are formed with use of the first thread and of the second thread. The two layers are connected to one another by the spacer threads during the knitting process. The density and arrangement of the spacer threads can be varied in order to adjust the compressive strength of the knitted spacer fabric in the height direction as desired.

Once the knitted spacer fabric has been produced, at least one predetermined separation point is formed in the first layer and in the second layer. The second thread is weakened and preferably severed along the predetermined separation point. The first thread is maintained along the predetermined separation point, such that the stitches in the layers do not come apart. The at least one first thread therefore is not severed along the predetermined separation point. The at least one second thread is weakened along the predetermined separation point by means of a physical and/or chemical influence. A weakening of the second thread can be achieved selectively on account of the different physical and/or chemical properties of the first thread and of the second thread.

In a preferred embodiment the at least one second thread is weakened along the at least one predetermined separation point by the introduction of energy, preferably heat. The energy is preferably introduced in a contact-free manner, for example with use of electromagnetic radiation, in particular a laser beam.

Alternatively or additionally to the introduction of energy, a chemical agent can be applied to the first layer and the second layer along the at least one predetermined separation point. The chemical agent can be alkaline or acidic, depending on whether the second thread is less alkali-resistant or less acid-resistant compared to the first thread. A selective weakening of a second thread can thus be achieved also by chemical means.

In a further aspect of the invention a textile 3D structure is proposed, also referred to as a knitted spacer fabric, having defined predetermined breaking points, the field of application of which comprises all automotive and non-automotive applications that require predetermined breaking points (in particular in airbag systems). This textile 3D structure can preferably have one or more of the following features in any combination:

-   -   the textile 3D structure can have different thicknesses;     -   the textile 3D structure can have an open or closed structure;     -   the upper and/or lower cover layers can be connected by spacer         threads (pile threads);     -   the upper and/or lower cover layers can be formed by stitch         formation by the same yarn types with counts >11 dtex in         different thread systems;     -   the yarns can differ in terms of count, texture, and chemical         basis;     -   in particular due to the chemical basis of the yarns, a         defined—also subsequently induced—reduction of the strength         (controlled weakening) and therefore an opening of the structure         in defined forms are made possible in the entire textile;     -   this controlled reduction of strength can be realised both         physically (laser, heat input) or as a result of (textile)         chemical influence (coating, spraying, dyeing, application by         doctor blade, pH value-dependent wetting of the fibres, acidic         or alkaline);     -   the forms created by the weakened fibres thus can be created         from predetermined break lines freely selectable         two-dimensionally in all directions and punctiform break lines         or interruptions (perforation), distributed over the entire area         of the cover layers and thickness of the knitted spacer fabric         products.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantageous embodiments of the invention will become clear from the dependent claims, the description, and the drawings. Preferred exemplary embodiments of the invention will be explained in detail hereinafter on the basis of the accompanying drawings, in which:

FIG. 1 shows a basic schematic illustration of wales and courses of an exemplary embodiment of a knitted spacer fabric,

FIG. 2 shows a schematic perspective view of a stitch or thread loop formed of a first thread and a second thread, as is formed in the first layer and the second layer of the knitted spacer fabric,

FIG. 3 shows a heavily schematised illustration of an exemplary embodiment of a knitted spacer fabric, as considered in a longitudinal direction parallel to the wales following production of the knitted spacer fabric in a knitting machine,

FIG. 4 shows a view of the knitted spacer fabric according to FIG. 3, wherein the formation of a predetermined separation point in each layer is shown schematically,

FIGS. 5 and 6 show stitches in a plan view of one of the layers in the illustration according to FIG. 1, wherein in each case a predetermined separation point is shown schematically.

DETAILED DESCRIPTION

FIGS. 3 and 4 each show an exemplary embodiment of a knitted spacer fabric 10 in heavily schematised manner. The knitted spacer fabric 10 has a first layer 11 and a second layer 12. The two layers, 11, 12 are each formed by a plurality of stitches 13, which form wales 14 in a longitudinal direction L and courses 15 in a transverse direction Q at right angles to the longitudinal direction L (FIG. 1).

In order to form each stitch 13, a first thread 16 and a second thread 17 are used. As is shown schematically in FIG. 2, the two threads 16, 17 are arranged side by side and are not directly connected to one another. They lie loosely against one another. In particular, the first thread 16 is not bonded to, intertwined or twisted with the second thread 17 or directly connected thereto in some other way.

The two threads have different chemical and/or physical properties and can be produced from different materials. The two threads 16, 17 are preferably synthetic fibres. In the exemplary embodiment shown here, both threads 16, 17 have the same thread thickness/yarn count, for example at least 11 dtex. For example, a plastics material, preferably polyester, polyamide or polypropylene, can be used as material for the threads 16, 17. In the exemplary embodiment shown here, the first thread is made of polyester having a high melting point and the second thread is made of polyester having a low melting point. The material of the first thread 16 thus has a higher melting point than the material of the second thread 17.

With use of the two threads 16, 17, the stitches 13 are formed both in the first layer 11 and in the second layer 12. The connection method can vary. The two layers 11, 12 are formed without weft threads. The wales 14 are connected to one another with use of the first thread 16 and the second thread 17 at the time of stitch formation. In accordance with the example, first threads 16 and second threads 17 fed via a common thread feed always alternate to and fro between two adjacent wales 14, and the threads 16, 17 in alternation, in successive courses 15, form a stitch 13 in one wale and then a stitch 13 in the next course 15 in the other wale 14. This connection is shown schematically in FIGS. 1, 5 and 6. As has already been explained, other connection methods can also be used. FIGS. 1, 5 and 6 show views in the height direction H of the outer side of the first layer 11 or the second layer 12.

The first layer 11 and the second layer 12 of the knitted spacer fabric 10 are arranged at a distance from one another in a height direction H, at right angles to the longitudinal direction L and at right angles to the transverse direction Q. The distance between the two layers 11, 12 can vary depending on the desired thickness of the knitted spacer fabric 10.

The first layer and the second layer 12 are connected to one another by connection threads 21. The number and arrangement of the connection threads 21 per unit of area in a plane spanned by the longitudinal direction L and the transverse direction Q can vary in order to achieve the desired compressive strength of the knitted spacer fabric in the height direction H.

The material of the connection thread 21 can correspond to the material of the first thread 16 and/or the second thread 17. It is also possible to form the at least one connection thread 21 by a further, third thread, which differs from the first thread 16 and the second thread 17 in respect of the material and/or the physical properties and/or the chemical properties.

In the exemplary embodiment shown here in a heavily schematised manner in FIGS. 3 and 4, the connection threads 21 each run in rows arranged in the longitudinal direction L between a wale 14 of the first layer 11 and a wale 14 of the second layer 12. This is what is known as an I-loop. In contrast to the shown exemplary embodiment, the connection threads 21 could also run in the transverse direction Q at an incline between wales 14 of the two layers 11, 12 not arranged directly one above the other in the height direction H.

In accordance with the invention at least one predetermined separation point 22 is formed in the first layer 11 and in the second layer 12 of the knitted spacer fabric 10. The predetermined separation point 22 can extend for example between two wales 14 in the longitudinal direction L (FIG. 5) or along a course 15 in the transverse direction Q (FIG. 6). The at least one predetermined separation point 22 can also run in a curved and/or angled manner at one or more points or can describe a free-form path. The extent of the predetermined separation point 22 within the plane spanned by the longitudinal direction L and transverse direction Q in principle can be selected arbitrarily. A predetermined separation point 22 in the first layer 11 and a predetermined separation point 22 in the second layer 12 are preferably aligned with one another as considered in the height direction H, such that the two layers 11, 12 tear or are separated at the same point so to speak in the event of a tensile load above a threshold value.

The at least one second thread 17, which crosses the predetermined separation point 22, is weakened and in accordance with the example severed along the predetermined separation point 22. The tensile strength of the knitted spacer fabric 10 in the first layer 11 and in the second layer 12 is therefore determined along the respective predetermined separation point 22 substantially merely by the first thread 16, whereas the second thread 17 makes no contribution or merely a small contribution to the tensile strength. The tensile strength of the connection outside the at least one predetermined separation point 22 is thus greater. In the event of a loading of the knitted spacer fabric 10 with an appropriate tensile force, the knitted spacer fabric 10 in the first layer 11 and in the second layer 12 therefore tears along the at least one predetermined separation point 22.

In order to weaken the at least one second thread 17 along the at least one predetermined separation point 22, energy is introduced in the form of heat in the exemplary embodiment described here. As is shown in a heavily schematised manner in FIG. 4, heat can be introduced in a contact-free manner by means of electromagnetic radiation and in accordance with the example by means of a laser beam 23 of a laser 24. The introduction of heat can be implemented in the first layer 11 and in the second layer 12 simultaneously or chronologically in succession. The laser 24 or the laser beam 23 is guided over the path describing the predetermined separation point 22 and is moved along the respective layers 11, 12 and introduces heat into the first thread 16 and the second thread 17.

Here, heat is introduced in such a way that the second thread 17 is heated at least to a temperature corresponding to the melting point of the material of the second thread 17 and below the melting point of the material of the first thread 16. The at least one second thread 17 is thus significantly weakened in respect of its tensile strength along the predetermined separation point 22 and is severed in the exemplary embodiment. The at least one second thread 17 does not necessarily have to be severed. Plastic deformation is also sufficient, said deformation reducing the thread thickness d by at least 30% or at least 50% or at least 70% and/or causing a plastic elongation along the direction of extent of the second thread 17. With an increased length of the at least one second thread 17, in the event of a tensile force, substantially no tensile force can initially be taken up by the second thread 17 until the first thread 16 has torn. Thus, if the second thread 17 is not fully severed, the first thread 16 and the second thread 17 can tear sequentially in the event of a sufficiently great tensile load, if the second thread 17 has been stretched lengthwise at the predetermined separation point 22 by the introduction of energy, for example heat.

The at least one second thread 17 can be weakened along the at least one predetermined separation point 22 also by other means, alternatively to the introduction of energy, for example heat. For example, an alkaline agent or acidic agent can be applied along the at least one predetermined separation point 22. In an embodiment of this kind, the acid resistance and/or alkali resistance of the material of the first thread 16 is greater than that of the second thread 17. The exposure time of the acidic or alkaline agent at the at least one predetermined separation point 22 is selected in such a way that the connection by the first thread 16 at the at least one predetermined separation point 22 is maintained, whereas the tensile strength of the at least one second thread 17 is significantly reduced or the at least one second thread 17 is completely severed at the at least one predetermined separation point 22. After a sufficient exposure time, the alkaline or acidic agent at the predetermined separation point 22 can be washed off for example, so as to avoid causing damage to the first thread 16.

The course of the predetermined separation point 22 in the respective planes 11, 12 can be achieved along an arbitrary path by introduction of energy and/or application of an alkaline or acidic substance. A template can be used to introduce the energy and/or to apply a chemical agent to the at least one predetermined separation point 22. A chemical agent can be applied for example by doctor blade. A chemical agent can also be applied within the scope of a dyeing of the knitted spacer fabric 10.

In the preferred exemplary embodiment of the knitted spacer fabric 10 described here, a predetermined separation space 25 is defined between a predetermined separation point 22 in the first layer 11 and an associated predetermined separation point 22 in the second layer 12 (FIG. 4). The predetermined separation space 25 is not traversed by connection threads 21 in the case of predetermined separation points 22 extending in the longitudinal direction L in the first layer 11 and in the second layer 12. The tearing of the knitted spacer fabric 10 along the predetermined separation points 22 therefore is not hampered or hindered by the connection threads 21.

With different extents of the predetermined separation points 22, the predetermined separation space 25 can be traversed by one or more connection threads 21. In an embodiment of this kind, the at least one connection thread 21, which crosses the predetermined separation space 25, can be weakened or severed in the region of the crossing point of the predetermined separation space 25. For example, the at least one connection thread 21 can be produced for this purpose from the same material as the second thread 17 and can be weakened or severed by the action of a physical and/or chemical means, similarly to the manner described previously in conjunction with the second thread 17 at the predetermined separation point 22.

The invention relates to a knitted spacer fabric 10 and a method for producing same. The knitted spacer fabric 10 has a first layer 11 formed by stitches 13, a second layer 12 formed by stitches 13, and connection threads 21, which connect the two layers 11, 12 arranged at a distance from one another in a height direction H. At least one predetermined separation point 22 is formed in each layer, at which point the tensile strength is reduced. The stitches 13 are formed in each case by a thread bundle comprising a first thread 16 and a second thread 17. The threads 16, 17 have different physical and/or chemical properties, for example different melting points, different resistances to alkaline or acidic agents, etc. The second thread 17 can thus be selectively severed at the at least one predetermined separation point 22 or weakened in respect of its tensile strength, whereas the at least one first thread 16 is not severed at the predetermined separation point 22 and preferably does not experience a significant reduction of its tensile strength.

LIST OF REFERENCE SIGNS

-   10 knitted spacer fabric -   11 first layer -   12 second layer -   13 stitch -   14 wale -   15 course -   16 first thread -   17 second thread -   21 connection thread -   22 predetermined separation point -   23 laser beam -   24 laser -   25 predetermined separation space -   d thread thickness -   H height direction -   L longitudinal direction -   Q transverse direction 

1. A knitted spacer fabric (10) comprising: a first layer (11) comprising first layer stitches (13) and a second layer (12) comprising second layer stitches (13), wherein the first layer stitches (13) and the second layer stitches (13) form wales (14) in a longitudinal direction (L) and form courses (15) in a transverse direction (Q) at right angles to the longitudinal direction (L), wherein the first layer stitches (13) and the second layer stitches (13) stitches (13) are formed by a thread bundle comprising a first thread (16) and a second thread (17), which are placed side by side without direct connection, wherein the first layer (11) and the second layer (12) are arranged at a distance from one another and are connected to one another by connection threads (21) in a height direction (H) at right angles to the longitudinal direction (L) and the transverse direction (Q), wherein the second thread (17) is severed and/or weakened in respect of its tensile strength in the first layer (11) and the second layer (12) along at least one predetermined separation point (22).
 2. The knitted spacer fabric according to claim 1, wherein the first thread (16) and the second thread (17) are made of different materials.
 3. The knitted spacer fabric according to claim 1, wherein the first thread's (16) material has a higher melting point than the second thread's (17) material.
 4. The knitted spacer fabric according to claim 1, wherein the first thread's (16) material has a better alkali resistance than the second thread's (17) material.
 5. The knitted spacer fabric according to claim 1, wherein the first thread's (16) material has a better acid resistance than the second thread's (17) material.
 6. The knitted spacer fabric according to claim 1, wherein one or both of the first layer (11) and the second layer (12) are formed without weft threads.
 7. The knitted spacer fabric according to claim 1, wherein the connection threads (21) do not cross a predetermined separation space (25) defined by paired predetermined separation points (22) of the at least one predetermined separation point (22) in the first layer (11) and the second layer (12).
 8. The knitted spacer fabric according to claim 1, wherein a connection thread (21) of the connection threads (21), which crosses a predetermined separation space (25) defined by paired predetermined separation points (22) of the at least one predetermined separation point (22) in the first layer (11) and the second layer (12), is made of a same material as the second thread (16).
 9. A method for producing a knitted spacer fabric (10) according to claim 1, said method comprising: producing the knitted spacer fabric (10) comprising the first layer (11), the second layer (12) and the connection threads (21) connecting the the first layer (11) and the second layer (12), generating the at least one predetermined separation point (22) in the first layer (11) and/or the second layer (12) by weakening the at least one second thread (17) along the at least one predetermined separation point (22), wherein the weakening is achieved by a physical and/or chemical influence.
 10. The method according to claim 9, wherein the influence comprises introduction of energy into the at least one second thread (17) along the at least one predetermined separation point (22).
 11. The method according to claim 9, wherein the influence comprises application of a chemical agent to the at least one second thread (17) along the at least one predetermined separation point (22). 